1. Field of the Invention
This invention relates to photosensitive compositions containing dispersed inorganic particulate material and particularly relates to photopolymer compositions containing such particulate matter. More particularly, it relates to photopolymerizable paste compositions suitable for screen printing and firing using thick film techniques.
2. Description of the Prior Art
Metallizing compositions containing finely divided noble metal or dielectric inorganic particulate material are well known for use in the art of preparing conductor and dielectric patterns or layers on substrates. Similarly, photoresist compositions are well known in the art for producing resist patterns on substrates and subsequent treatment of the substrate in the areas which have been imagewise exposed and developed. U.S. Pat. No. 3,573,908 discloses a process for the preparation of a ceramic substrate glaze using a mixture of a photoresist, a multicomponent oxide glaze frit, and a solvent. British Pat. No. 1,256,344 discloses applying a combination of a particulate metal, glass binder, photosensitive material, and solvent on the surface of the substrate and drying, exposing and developing it. The pattern provided is then fired to produce a printed circuit.
The photosensitive compositions containing inorganic particulate material of the prior art have not found wide acceptance in the electronic industry for fabricating electronic circuits, as they are not readily compatible with either thin film or thick-film techniques commonly employed for that purpose. The photopolymerizable paste compositions of this invention and their process of use by screen printing are readily compatible with commonly employed thick-film techniques and systems used for fabricating electronic circuits. The compositions of the invention due to the uniform dispersion and suspension of constituents may be prepared and packaged as paste, suitable for screen printing thus obviating the requirement that the circuit manufacturer become involved with the mixing of photoresist solutions, the dispersion of the inorganic particulate material in the resist composition, and complex coating of the composition on substrates. Additionally, screen printing the compositions provide for application on selected areas of substrate, thus substantially reducing the waste and increasing yields. This can be very important where the inorganic particulate material is a valuable noble metal, e.g., gold, silver, palladium or platinum.